For large liquid containers, how to discharge liquid held inside is a common problem for users. For example, to ensure water quality, liquid in an aquarium tank is required to be changed at regular intervals. The common method of discharging liquid in a liquid container adopted by the prior art includes machine discharge and artificial discharge. As to the former, liquid in a container is discharged with water pump. As to latter, the simplest way is to scoop liquid continuously out from the container with a small container, such as water ladle or large spoon. Another commonly used artificial discharge method is to discharge liquid in a container with water pipe based on the siphon principle. However, no matter which of the above methods is adopted, discharge process is required to be monitored by people, so labor cost is essential. In particular, for the liquid discharge of an aquarium tank, water is required to be changed, without catching aquatic animals in the tank. Usually, liquid in the aquarium tank is required to be discharged quantitatively, instead of fully discharged, and amount of the water discharged is also required to be adjusted correspondingly. Therefore, liquid discharge process of the aquarium tank is required to be monitored more. Yet, with regards to the places with concentrated breeding of aquatic animals, there are different requirements on discharge volume for each aquarium tank. Nevertheless, with the liquid discharge method of the prior art, great amount of personnel are more needed for specialized monitoring of the discharge process. Thereby, labor cost is greater.
Therefore, a technology that can make liquid discharge operators free from being troubled by liquid discharge monitoring is required.